Ice stream

“ This must have been about two hundred and fifty years ago, since the distance from the sea to where the break occurs in the mountain-chain through which the ice-stream emerges into the valley is about ten miles. We see it then just appearing, and we watch its progress through this long time. Its front is hundreds of feet high and miles across. We observe the icy flood moving steadily and irresistibly onward, over precipices, down steep declivities, upon level plains—sometimes advancing with comparative rapidity, sometimes slowly, but steadily, year by year, coming towards the fiord. ”

“ In direct opposition, as it would seem, to the laws of the propagation of heat, the ice in running water frequently begins to form at the bottom of the stream instead of the top; and this fact, while it is received with doubt by some, even among the scientific, is frequently attested by those whose business leads them to observe the phenomenon connected with rivers. Millers, fishermen, and watermen find that the masses of ice with which many rivers are crowded in the winter season rise from the bottom or bed of the stream. ”

“ Naturally when the ice stream reaches the lower and warmer altitudes, melting goes on more rapidly, until finally the end of the ice wastes away, and a stream or river ensues. Now, it is for only a very short time in each year, in the latitude that we are considering, that the temperature is such that the amount of daily melting of ice exactly corresponds with the daily advance produced by the flow of the glacier. ”

“ At last, down the stream came an immense mass of ice, and, striking the barrier about at its centre, it gave way, and the whole was swept onward together, leaving the river entirely free, with only here and there a cake of ice floating quietly along. The great accumulation, in its downward course, hit against a tree that stood in mid-current, and caused it to quiver like a reed; and it swept quite over the shrubbery that bordered what, in summer-time, is the river's bank, but which is now nearly the centre of the stream. ”

“ A stream is a drifting line of drift ice. A tongue is a projecting point of ice, under water. A calf is a mass of loose ice lying under a floe near its margin, and, when disengaged from that position, rising with violence to the surface. Brash ice consists of fragments and nodules, the wreck of other kinds of ice, and sludge is the term applied to smaller pieces, generally saturated by the sea.
A bright white line on the horizon, seen over an ice-field, and denoting more ice, is known as the ice-blink. Over land or large masses of ice it generally has a yellowish tinge. ”

“ In regions where the winters are very cold the effect of ice on the development of the stream beds both in the torrent and river sections of the valley is important. This work is accomplished in several diverse ways. In the first place, where the stream is clear and the current does not flow too swiftly, the stones on the bottom radiate their heat through the water, and thus form ice on their surfaces, which may attain considerable thickness. As ice is considerably lighter than water, the effect is often to lift up the stones of the bed if they be not too large ”

“ But when the water is rising rapidly, as now, and especially if there is a strong wind, like this, to increase the motion, as it does either by outward pressure, or by forcing the air through the chinks in under the ice, I have always noticed that the stream acts on the ice at a much less height, and much more powerfully, than when the rise is slow and the weather calm. ”

“ Under the ice river is always flowing a stream of water, and many air holes and openings are found upon the surface at different points, no doubt produced by the influence of spring water coming in of temperature above freezing or at the usual fifty-two degrees, about the average of fresh water springs in all latitudes. This conglomeration of influences to make a glacier shows the absurdity of having such solid masses break off, as claimed to be seen by Arctic explorers, large enough to remain intact well down into the Atlantic Ocean. ”

“ The stream which lies farthest to windward drives faster and is driven on to the stream under its lee. Stream joins stream, and as the storm increases we have a formidable "body of ice" many miles in width as well as breadth. This pack drives on and on, resistless and all-conquering, until it is checked in its steady career by meeting another solid pack, or by the land, or, in the Antarctic, by one of those giant bergs. Confusion arises; the ice piles itself high up on the land—great heaps of even 20 or 30 feet high being formed. ”

“ All this ice, each piece different from its neighbour, is driven together by the wind and sea, and is formed into "streams" of ice, which always lie at right angles to the wind and which may be many miles in length. Loose pieces of ice in the open sea, on the weather side of these "streams," are driven before the wind more quickly than the stream itself, and are ultimately driven into the stream and form part of it. ”

“ This intense heat during the day melts the surface of the ice, which forms streams that run along on the top of a glacier until they come to a crevasse or riffle in the ice river, where they plunge down and become a part of the glacial stream that is flowing underneath the ice. ”

“ The dynamical conditions necessary are probably a sudden breaking up of the ice before it is rotted by thawing and a flood to wield it. The proper conditions do not often occur in our present Western streams. Usually the striæ are parallel, as much so as in glacial action, and commonly on surfaces dipping up stream, but occasionally upon limited areas dipping down stream. ”

“ Sludge consists of a stratum of detached ice crystals, or of snow, or of the smaller fragments of brash-ice, floating on the surface of the sea.
A stream is an oblong collection of drift or bay-ice, the pieces of which are continuous. It is called a sea-stream when it is exposed on one side to the ocean, and affords shelter from the sea to whatever is within it. ”

“ Be that as it may, its power of excavation on a level is proved, as I showed in my last letter, to be zero. Your correspondent thinks the glacier power vanishes towards the extremity; but as long as the ice exists, it has the same progressive energy, and, indeed, sometimes, with the quite terminal nose of it, will plough a piece of ground scientifically enough; but it never digs a hole: the stream always comes from under it full speed downhill. ”

“ When one of the above-mentioned frosts occurs, the stone which composes the weir soon becomes incrusted with ice, which increases so rapidly in thickness as in a short time to impede the course of the stream, which falls over it in a tolerably uniform sheet, and with considerable velocity; at the same time, the wind blowing strongly from the north-west, contributes to repel the water and freeze such as adheres to the crest of the weir when its surface comes nearly in contact with the air. ”

“ The open pools can no longer be called pools; they are great rivers, whose hummock-lined shores look dimly through the haze. Contrasted with the pure white snow, their waters are black even to inkyness; and the silent tides, undisturbed by ripple or wash, pass beneath a pasty film of constantly forming ice. The thermometer is at 10°. Away from the ship, a long way, I walked over the older ice to a spot where the open river was as wide as the Delaware. Here, after some crevice-jumping and tickly-bender crossing, I set myself behind a little rampart of hummocks, watching for seals. ”

“ Standing on our little deck, and looking out on the floe, we had the strange spectacle of an undulating solidity, a propagated wave borne in swell-like ridges, as if our ice was a carpet shaken by Titans. I can not convey the effect of this sublime spectacle. The ice, broken into polyhedric masses, gave at a few hundred yards no indications to the eye of the lines of separation; besides which, the infiltration of salt water had no doubt increased the plasticity of the material. ”

“ While the rivers run perfectly clear and bright under the ice in the winter, in summer the turbid water of nearly all our large streams introduces another difficulty, and photographic operation must sometimes be deferred for weeks, unless the rain barrels be full or enough ice be found in the ice-house, over and above the domestic needs, to serve. ”

“ The fierce sun of summer sends millions of tiny streamlets down into its interior, which collect, augment, cut channels for themselves through the ice, and finally gush into the plain from its lower end in the form of a muddy river. Even in winter this process goes on, yet the ice-river never melts entirely away, but holds on its cold, stately, solemn course from year to year—has done so for unknown ages, and will probably do so to the end of time. ”

“ But we shall see that here, as in the world of man, appearances are deceitful, and that the glacier well deserves to be called an ice-river, in allusion to its regular and continuous motion.
Between the snow-fall in the higher regions of the globe, and the quantity of snow which every summer disappears through liquefaction, the difference is very considerable. The supply, so to speak, exceeds the demand, and a residuum is annually left. It is only below the perpetual snow-line that the snow created and accumulated in winter is wholly melted in the warm season. ”

“ The strange openings in the water of a « 124 » few hours ago are now great rivers, lined by banks of hummocks, and wreathed in frost smoke. The continually increasing wind from the northward explains this southern drift of the ice, and with it these unwelcome openings. We are stationary, and the detached ice is leaving us. ”

“ The air is expelled from the water during freezing, if opportunity is found for it to do so. Unless this is done, the ice is cloudy. Agitation of the water assists the escape of the air; hence it is that ice from running streams is usually clearer and more brilliant than pond or lake ice. An outlet afforded to the land-locked ponds and lakes is often beneficial during ice-making weather. Too rapid a current, however, will retard growth, and a gentle motion diffused over the entire field produces the best results. ”

“ The strong floe of ice-table under ice-table, and hummock upon hummock, makes our position one of nearly complete solidity. We are glued up in ice; and to liberate us, some fearful disruption must take place. Twenty-five feet of solid ice is no feeble matrix, for a brig drawing but ten. Yet the water is wider, and still widening around us; so that now we hold on—that is, our floe holds on, to the great mass to the north of us, like a little peninsular cape.
“To the south every thing is in drifting motion—water, sludge, frost-smoke—but no seals. ”

“ As the river freezes first at its most northerly point, and this belt of solid ice is gradually extended south, or back towards its source, the floating cakes of its upper reaches, borne by the swift current, are piled on the ever-advancing barrier in confused masses that stretch across the river like windrows. ”

“ As our rivers are continually pouring their streams into the ocean, so many of the glaciers or ice-rivers of the Arctic zone, descending to the water-edge, are slowly but constantly forcing themselves farther and farther into the sea. In the summer season, when the ice is particularly fragile, the force of cohesion is often overcome by the weight of the prodigious masses that overhang the sea or have been undermined by its waters ”

“ When the sea freezes at the base of a lofty precipice, the sheet of ice is prevented from adhering to the land by the rise and fall of the tide. Nevertheless, it often continues on the shore at the foot of the cliff, and receives accessions of drift snow blown from the land. Under the weight of this snow the ice sinks slowly if the water be deep, and the snow is gradually converted into ice by partial liquefaction and re-congelation. In this manner, islands of ice of great thickness and many leagues in length, originate, and are eventually blown out to sea by off-shore winds. ”

“ After the melting of the snow there appears besides a number of inequalities, and the clefts previously covered with a fragile snow-bridge now gape before the wanderer where he goes forward, with their bluish-black abysses, bottomless as far as we can depend on ocular evidence. At some places there are also to be found in the ice extensive shallow depressions, down whose sides innumerable rapid streams flow in beds of azure-blue ice, often of such a volume of water as to form actual rivers. ”

“ The stillness far out on the great ice-field is immediately noticed by one who has recently traversed the sloping surfaces of the tributary glaciers. It is always silent on that vast frozen plateau. There are no surface streams and no lakes; not a rill murmurs along its channel of ice; no cascades are formed by streams plunging into moulins and crevasses. The water produced by the melting of the ice finds its way down into the glacier and perhaps to its bottom, and must there form rivers of large size; but no indications of their existence can be obtained at the surface. ”

“ The river don't freeze over all at once—the ice floats down and jams and stops and the bare places between freeze over; but when the ice jams, it crumples up on the edges and makes ridges, and it is where the ridges are that the snow banks up into drifts. Sometimes the drifts are all around a smooth sheet of ice, and then when the snow begins to melt, the smooth ice turns into a sort of pond, and maybe the water on top of the ice is an inch deep and maybe it is more. ”